This invention relates to a method of treating polyester material to improve its adhesion to rubber, particularly by using a treating composition which contains an epoxy compound and a melamine compound, followed by heat treatment of the polyester material at a temperature of 100.degree.-250.degree. C.
Polyester fibers have excellent tensile strength, dimensional stabilty, heat resistance and water resistance. It has many properties that make it desirable for use as a reinforcing material for rubber.
However, polyester fibers have a great shortcoming on that their adhesion to rubber is inferior to that of polyamide fibers such as nylon 6, nylon 66, which are also representative industrial fibers.
Thus, polyamide fibers achieve a very good adhesion to rubber simply by treating them with a resorcinol-formaldehyde-rubber latex (RFL) adhesive; in the case of polyester fibers, good adhesion is not achieved by this RFL treatment.
For this reason, numerous attempts have been made to improve the adhesion of polyester fibers to rubber. Typical methods are as follows: RFL treatment, i.e., the dip treatment of the fabric of the greige cord, is given after pretreatment with an adhesive such as an epoxy compound, an isocyanate compound, an ethylene urea compound; in the dip treatment, the RFL is mixed with an esterophilic component such as a novolak resin, 2, 6-bis (2', 4'-dihydroxyphenylmethyl)4-chlorophenol, known by the trade name of Pexul; and (2) an adhesive such as an epoxy compound or an isocyanate compound is applied at the yarn stage followed subsequently by the dip treatment with RFL. In the former method, the desired adhesion is achieved to a certain extent but the amount of adhesive used becomes large and the treating procedure becomes complicated, resulting in increased costs. The latter method has a practical advantage in that, like with polyamide fibers, only RFL treatment is necessary; but adhesion, which is the key requirement, is somewhat unsatisfactory. Consequently, in the latter method, a new problem is created that, in order to increase adhesion, the yarn treatment must be performed under impractical conditions, e.g., the concentration of the adhesive is markedly increased or heat treatment is made extremely severe.